The invention relates to a luminaire comprising a housing which defines an internal space containing at least one light source formed by a light-emitting diode (LED) and optical means for guiding the light emitted by the LED to the exterior of the housing.
Such a luminaire is known from the document WO 98/33007. This luminaire, designed for street lighting, utilizes light emitted by LEDs: the optical guiding means used ensure on the one hand a concentration of the luminous intensity produced by the LED into a beam and on the other hand a defined direction of the beam.
The emission characteristic of a LED has a special shape. The optical means, which operate by principles of physical optics, have a geometry which renders it possible to obtain an optimum performance, provided the optical means occupy an accurate and constant position with respect to the emission characteristic of the LED. Since the luminaire is to be first transported and then installed, the robustness of the mounting of the optical means with respect to the LED must be guaranteed if the luminaires are to maintain the properties claimed by the manufacturer.
In the document WO 98/33007, the LED is fixed inside the optical means, which in their turn are fixed to the housing. The realization of this construction necessitates delicate manipulations of the LED. The LEDs, however, are highly sensitive to mechanical manipulations: their operational life and their light-emission performance depend on the care with which they are handled, especially during their mounting inside a luminaire as described in the opening paragraph. The LED comprises, among other things, a fragile dome on which no major forces are allowed to be exerted. A delicate mounting operation such as the one proposed in the document WO 98/33007 is accordingly to be avoided. In addition, this mounting is time-consuming and costly in terms of automated operations.
It is an object of the invention to resolve to a high extent the problem of mounting the optical means relative to the LED inside the luminaire.
According to the invention, a luminaire as described in the opening paragraph is for this purpose characterized in that the LED is mounted to a support connected to the housing, and in that the optical means are held between a retaining element connected to the housing and the support of the LED.
The mounting thus realized involves a placement of the optical means on the support of the LED and the use of the retaining element connected to the housing for keeping it fixed. This mounting provides the advantages that no delicate manipulations of the LED are necessary because the latter may be pre-installed on its support, that it is fast, and that it can be readily automated.
In an embodiment of the invention, the optical means are elastically held between the retaining element connected to the housing and the support of the LED by elastic retention means. Said elastic retention means in cooperation with the retaining element connected to the housing then exert a pressure on the optical means. As a result, the optical means exert a pressure on the support of the LED. Any mechanical play which may exist between the retaining element connected to the housing and the optical means and between the optical means and the support of the LED is eliminated, and this prevents relative movements of the optical means with respect to the support of the LED. The shapes of the optical means and those of the support of the LED are advantageously adapted such that, under pressure, the contact between the optical means and the support of the LED will serve to guarantee a precise and constant position which causes the assembly to provide an optimum performance.
In a preferred embodiment of the invention, the elastic retention means of the optical means are realized in the form of a block of elastic material placed in a position such that it is compressed between the retaining element connected to the housing and the optical means. Said elastic material may in particular be one of any number of foam types. This solution has the advantages that it is simple in its implementation and that it renders it possible to control the intensity of the pressure exerted by the optical means on the support of the LED through the choice of the characteristics of the elastic material used.
In an advantageous embodiment of the invention, a material having a low adhesion coefficient is placed between the optical means and the retaining element connected to the housing. This material achieves the contact between the optical means and either the retaining element of the optical means or the elastic retention means. The effect of this material of low adhesion coefficient, which may be polyethylene, is to facilitate relative translatory movements at the level of contact between the optical means and either the retaining element connected to the housing or the elastic retention means. Translatory movements of the retaining element connected to the housing or of the elastic retention means with respect to the housing on which the support of the LED is fixed may in fact carry the optical means along with them, which optical means in that case will be shifted from their position of optimum performance in relation to the emission characteristic of the LED. Said translatory movements resulting in shifts at the level of contact between objects may be the result of an external mechanical stress such as that caused by differences in thermal expansion between different materials. The differences in expansion are indeed the source of relative movements between certain objects in this environment, in which said objects made from different materials are present and in which the temperature is made to vary considerably, which movements may not be negligible.
In an advantageous embodiment of the invention, the retaining element connected to the housing is connected to the housing by gluing means. This solution avoids the necessity of using screws. Screws are habitually used in the field of luminaires, but they cause problems in relation to differences in expansion when the materials joined together are different, which is generally the case with a luminaire as described in the opening paragraph. An additional advantage is that a greater miniaturization of the luminaire is rendered possible than can be achieved with screws, because the use of gluing means requires a certain surface area but does not occupy a substantial volume of material.
In a special embodiment of the invention, the gluing means are formed by adhesive tapes.
In a particularly advantageous embodiment of the invention, the retaining element connected to the housing is a plate which transmits light. This arrangement is advantageously chosen when the light-transmitting plate is laid over the optical means, because in that case it fulfills two functions: it protects the optical means, which are usually fragile, and it keeps said optical means in place.